Field of the Invention and Related Art Statement
The present invention relates to a hyperthermia apparatus for use in a thermotherapy in which malignant body tissues, particularly cancer tissues are necrosed by selectively heating them with electric fields at high frequencies.
The hyperthermia apparatus has been developed to necrose cancer tissues by heating them above a temperature higher than 45.degree..about.43.degree. C. due to the fact that the cancer tissues are liable to be damaged by heat rather than normal tissues. There have been proposed various types of hyperthermia apparatuses.
For instance, in Japanese Patent Publication Kokai No. 59-135,066, there is disclosed a hyperthermia device comprising a single inside-body electrode and a single outside-body electrode. This type of hyperthermia apparatus has been manufactured and sold by Kureha Kagaku Kogyo Co., Ltd. in Japan under the trade name of Endoradiotherm 100A. In U.S. Pat. No. 1,350,168 and Japanese Utility Model Publication No. 58-8,254, there is described another type of hyperthermia apparatus comprising a plurality of outside-body electrodes which are arranged around the patient's body and a switching means for selectively using a pair of electrodes which are faced to each other via the body of the patient.
FIG. 1 is a schematic view illustrating the known hyperthermia apparatus disclosed in said Japanese Patent Publication Kokai No. 59-135,066. In this known hyperthermia apparatus an inside-body electrode 4 is inserted into a cavity 2 of a patient's body 1 and an outside-body electrode 5 is placed on the outer surface of the body such that these electrodes are faced to each other via a cancer 3. Across the inside-body electrode 4 and outside-body electrode 5 is applied an RF electric power from an RF oscillator 6 to generate an electric field at a high frequency within the patient's body 1, and then a portion of the body 1 between these electrodes is heated by the electromagnetic induction. The electrode 4 is inserted into the cavity 2, so that its surface area is much smaller than that of the electrode 5. Therefore, the density of the high frequency electric field becomes higher toward the inside-body electrode 4.
FIG. 2 is a schematic view illustrating another known hyperthermia apparatus including a plurality of outside-body electrodes. This type of apparatus is disclosed in the above mentioned Japanese Utility Model Publication No. 58-8,254. In this known hyperthermia apparatus, on an outer surface of a patient's body 1, there are arranged outside-body electrodes 7 and 8 such that a cancer 3 is sandwiched by these electrodes. Then, an RF electric power is applied across the electrodes 7 and 8 from an RF oscillator 9 to generate an electric field of high frequency so that a portion of the body 1 between the electrodes 7 and 8 is selectively heated by the electromagnetic induction.
In the known hyperthermia apparatus illustrated in FIG. 1, since the density of the higy frequency electric field is increased toward the inside-body electrode 4, the body is preferably heated locally. However, this local heating has a demerit in some applications and a part of the cancer 3 may not be heated due to an error in the positioning of the electrodes or due to the size of the cancer 3. For instance, in the esophagus where a long cancer is liable to from in a longitudinal direction of the esophagus, it is practically impossible to heat the whole cancer to a predetermined temperature, and a part of the cancer is therefore not sufficiently heated. Then, this part of the cancer may not be necrosed, and grows. Moreover, since there is provided only one outside-body electrode 4, when a plurality of cancers are existent around the patent body 1, it is necessary to rearrange the electrode 4, which makes the operation cumbersome.
In the known hyperthermia apparatus depicted in FIG. 2, the outside-body electrodes 7 and 8 may have a relatively large surface area, so that the cancer 3 having a large area can be heated to the effective temperature. However, the high frequency electric field is spread widely between the large electrodes, and thus the normal tissues surrounding the cancer tissues might be heated to a higher temperature. Therefore, the hyperthermia apparatus could not be used for a long time period. As is well known in the art, the effect of the thermotherapy depends on not only the temperatures to which the tissues are heated, but also upon the time period for which the tissues are held at such temperatures. In this known hyperthermia apparatus, in order not to heat the normal tissues excessively, there is provided a cooling means of a large scale at the electrode. This results in the whole electrode becoming complicated in construction and large in size.
In the known hyperthermia apparatus described in the above mentioned U.S. Pat. No. 4,350,168, there is provided a cooling means beside an electrode in order to cool the patient body near the electrode. The coolimg means includes a balloon and a device for circulating cooling water through the balloon.
In the U.S. Pat. No. 4,350,168, there is also shown another hyperthermia apparatus including three pairs of outside-body electrodes and high frequency powers having mutual phase difference of 123.degree. being applied to respective pairs of electrodes. In this known appartus, three pairs of electrodes would operate just like a single pair of electrodes, so that the normal tissues near the electrodes might be heated to undesired high temperatures. Further, if more than three pairs of electrodes are provided the mutual phase difference of the driving signals becomes smaller, and a high frequency current might flow into adjacent electrodes so that all the electrodes would operate as a single pair of electrodes.
In Japanese Patent Publication Kokai 60-119,962, there is disclosed inside-body and outside-body applicators each including an electrode, a balloon surrounding the electrode and a device for circulating a cooling medium through the balloon. By using such applicators, the normal tissues can be prevented from being heated excessively. In this known hyperthermia apparatus, the cooling medium circulating device is commonly used for the balloons of both the inside-body and outside-body applicators. In this apparatus, in order to prevent the electrodes from being short-circuited, the cooling medium has to be made of an electrically insulating substance. However, if the electrode is surrounded by the insulating medium, the impedance between the electrodes is increased and the high frequency electric field may not be produced in the living body at a high efficiency and the tissues may not be heated to the desired high temperature. Therefore, an electrically conductive substance has to be used as the cooling medium, and thus there are provided separate devices for circulating the cooling mediums through respective balloons in order to avoid the short-circuiting. However, in the known hyperthermia apparatus these devices are not completely isolated from each other. For example, even if pipes connected to the balloons and pumps for circulating the cooling mediums through the balloons are provided separately, when the pumps and cooling devices are connected commonly to a power supply line, the cooling mediums might be electrically connected to each other by means of the power supply line, and the patient may not be protected against danger.
In Japanese Patent Publication No. 56-38,230, there is described still another known hyperthermia apparatus. In this known apparatus, there is arranged an automatic impedance matching circuit for matching an output impedance of a high frequency oscillator and an input impedance of a load circuit including electrodes to which is supplied high frequency electric power from the oscillator and the living body, so that the high frequency electric field can be generated efficiently in the living body.
Howwver, in such a known hyperthermia apparatus, there is not provided a protection means for the impedance mismatching at the start of applying the high frequency electric power, so that the electric device might be damaged by the high electric power reflected from the load due to the mismatching.
Moreover, in the known hyperthermia apparatus in which the electrodes are selectively switched into and out of the circuit, after switching the electrodes, the high frequency electric power is adjusted to have a desired amplitude and then is applied to the electrodes. However, the impedance of the load including the selected electrodes might vary due to various factors such as condition of the living body, contact condition of the electrodes to the body and connecting condition of the electrodes to connectors. Therefore, the impedance mismatching might be produced and the instrument might be damaged by the reflected high power. Further, the patient might be subjected to an electrical shock.